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    <title>Document</title>

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            height: 0;
            /* 兼容性 */
            line-height: 0;
            font-size: 0;


            /* border: 10px solid red; */
            /* border-top: 10px solid red;
            border-bottom: 10px solid greenyellow;
            border-left: 10px solid blue;
            border-right: 10px solid rgb(171, 250, 250); */
            border: 10px solid transparent;
            border-top-color: red;
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<body>
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